Answer:
see explanation
Step-by-step explanation:
Given that z² is directly proportional to w then the equation relating them is
z² = kw ← k is the constant of proportion
To find k use the condition z = 4 when w = 8, thus
4² = 8k
16 = 8k ( divide both sides by 8 )
2 = k
(i)
z² = 2w ← equation of proportion
(ii)
When w = 18, then
z² = 2 × 18 = 36 ( take the square root of both sides )
z = = 6
(iii)
When z = 5 , then
5² = 2w
25 = 2w ( divide both sides by 2 )
w = 12.5